PrintfFormatString.cpp revision 234353 
1//== PrintfFormatString.cpp - Analysis of printf format strings --*- C++ -*-==//
2//
3//                     The LLVM Compiler Infrastructure
4//
5// This file is distributed under the University of Illinois Open Source
6// License. See LICENSE.TXT for details.
7//
8//===----------------------------------------------------------------------===//
9//
10// Handling of format string in printf and friends.  The structure of format
11// strings for fprintf() are described in C99 7.19.6.1.
12//
13//===----------------------------------------------------------------------===//
14
15#include "clang/Analysis/Analyses/FormatString.h"
16#include "FormatStringParsing.h"
17
18using clang::analyze_format_string::ArgTypeResult;
19using clang::analyze_format_string::FormatStringHandler;
20using clang::analyze_format_string::LengthModifier;
21using clang::analyze_format_string::OptionalAmount;
22using clang::analyze_format_string::ConversionSpecifier;
23using clang::analyze_printf::PrintfSpecifier;
24
25using namespace clang;
26
27typedef clang::analyze_format_string::SpecifierResult<PrintfSpecifier>
28        PrintfSpecifierResult;
29
30//===----------------------------------------------------------------------===//
31// Methods for parsing format strings.
32//===----------------------------------------------------------------------===//
33
34using analyze_format_string::ParseNonPositionAmount;
35
36static bool ParsePrecision(FormatStringHandler &H, PrintfSpecifier &FS,
37                           const char *Start, const char *&Beg, const char *E,
38                           unsigned *argIndex) {
39  if (argIndex) {
40    FS.setPrecision(ParseNonPositionAmount(Beg, E, *argIndex));
41  } else {
42    const OptionalAmount Amt = ParsePositionAmount(H, Start, Beg, E,
43                                           analyze_format_string::PrecisionPos);
44    if (Amt.isInvalid())
45      return true;
46    FS.setPrecision(Amt);
47  }
48  return false;
49}
50
51static PrintfSpecifierResult ParsePrintfSpecifier(FormatStringHandler &H,
52                                                  const char *&Beg,
53                                                  const char *E,
54                                                  unsigned &argIndex,
55                                                  const LangOptions &LO) {
56
57  using namespace clang::analyze_format_string;
58  using namespace clang::analyze_printf;
59
60  const char *I = Beg;
61  const char *Start = 0;
62  UpdateOnReturn <const char*> UpdateBeg(Beg, I);
63
64  // Look for a '%' character that indicates the start of a format specifier.
65  for ( ; I != E ; ++I) {
66    char c = *I;
67    if (c == '\0') {
68      // Detect spurious null characters, which are likely errors.
69      H.HandleNullChar(I);
70      return true;
71    }
72    if (c == '%') {
73      Start = I++;  // Record the start of the format specifier.
74      break;
75    }
76  }
77
78  // No format specifier found?
79  if (!Start)
80    return false;
81
82  if (I == E) {
83    // No more characters left?
84    H.HandleIncompleteSpecifier(Start, E - Start);
85    return true;
86  }
87
88  PrintfSpecifier FS;
89  if (ParseArgPosition(H, FS, Start, I, E))
90    return true;
91
92  if (I == E) {
93    // No more characters left?
94    H.HandleIncompleteSpecifier(Start, E - Start);
95    return true;
96  }
97
98  // Look for flags (if any).
99  bool hasMore = true;
100  for ( ; I != E; ++I) {
101    switch (*I) {
102      default: hasMore = false; break;
103      case '\'':
104        // FIXME: POSIX specific.  Always accept?
105        FS.setHasThousandsGrouping(I);
106        break;
107      case '-': FS.setIsLeftJustified(I); break;
108      case '+': FS.setHasPlusPrefix(I); break;
109      case ' ': FS.setHasSpacePrefix(I); break;
110      case '#': FS.setHasAlternativeForm(I); break;
111      case '0': FS.setHasLeadingZeros(I); break;
112    }
113    if (!hasMore)
114      break;
115  }
116
117  if (I == E) {
118    // No more characters left?
119    H.HandleIncompleteSpecifier(Start, E - Start);
120    return true;
121  }
122
123  // Look for the field width (if any).
124  if (ParseFieldWidth(H, FS, Start, I, E,
125                      FS.usesPositionalArg() ? 0 : &argIndex))
126    return true;
127
128  if (I == E) {
129    // No more characters left?
130    H.HandleIncompleteSpecifier(Start, E - Start);
131    return true;
132  }
133
134  // Look for the precision (if any).
135  if (*I == '.') {
136    ++I;
137    if (I == E) {
138      H.HandleIncompleteSpecifier(Start, E - Start);
139      return true;
140    }
141
142    if (ParsePrecision(H, FS, Start, I, E,
143                       FS.usesPositionalArg() ? 0 : &argIndex))
144      return true;
145
146    if (I == E) {
147      // No more characters left?
148      H.HandleIncompleteSpecifier(Start, E - Start);
149      return true;
150    }
151  }
152
153  // Look for the length modifier.
154  if (ParseLengthModifier(FS, I, E, LO) && I == E) {
155    // No more characters left?
156    H.HandleIncompleteSpecifier(Start, E - Start);
157    return true;
158  }
159
160  if (*I == '\0') {
161    // Detect spurious null characters, which are likely errors.
162    H.HandleNullChar(I);
163    return true;
164  }
165
166  // Finally, look for the conversion specifier.
167  const char *conversionPosition = I++;
168  ConversionSpecifier::Kind k = ConversionSpecifier::InvalidSpecifier;
169  switch (*conversionPosition) {
170    default:
171      break;
172    // C99: 7.19.6.1 (section 8).
173    case '%': k = ConversionSpecifier::PercentArg;   break;
174    case 'A': k = ConversionSpecifier::AArg; break;
175    case 'E': k = ConversionSpecifier::EArg; break;
176    case 'F': k = ConversionSpecifier::FArg; break;
177    case 'G': k = ConversionSpecifier::GArg; break;
178    case 'X': k = ConversionSpecifier::XArg; break;
179    case 'a': k = ConversionSpecifier::aArg; break;
180    case 'c': k = ConversionSpecifier::cArg; break;
181    case 'd': k = ConversionSpecifier::dArg; break;
182    case 'e': k = ConversionSpecifier::eArg; break;
183    case 'f': k = ConversionSpecifier::fArg; break;
184    case 'g': k = ConversionSpecifier::gArg; break;
185    case 'i': k = ConversionSpecifier::iArg; break;
186    case 'n': k = ConversionSpecifier::nArg; break;
187    case 'o': k = ConversionSpecifier::oArg; break;
188    case 'p': k = ConversionSpecifier::pArg;   break;
189    case 's': k = ConversionSpecifier::sArg;      break;
190    case 'u': k = ConversionSpecifier::uArg; break;
191    case 'x': k = ConversionSpecifier::xArg; break;
192    // POSIX specific.
193    case 'C': k = ConversionSpecifier::CArg; break;
194    case 'S': k = ConversionSpecifier::SArg; break;
195    // Objective-C.
196    case '@': k = ConversionSpecifier::ObjCObjArg; break;
197    // Glibc specific.
198    case 'm': k = ConversionSpecifier::PrintErrno; break;
199    // FreeBSD format extensions
200    case 'b': if (LO.FormatExtensions) k = ConversionSpecifier::bArg; break; /* check for int and then char * */
201    case 'r': if (LO.FormatExtensions) k = ConversionSpecifier::rArg; break;
202    case 'y': if (LO.FormatExtensions) k = ConversionSpecifier::iArg; break;
203    case 'D': if (LO.FormatExtensions) k = ConversionSpecifier::DArg; break; /* check for u_char * pointer and a char * string */
204  }
205  PrintfConversionSpecifier CS(conversionPosition, k);
206  FS.setConversionSpecifier(CS);
207  if (CS.consumesDataArgument() && !FS.usesPositionalArg())
208    FS.setArgIndex(argIndex++);
209  // FreeBSD extension
210  if (k == ConversionSpecifier::bArg || k == ConversionSpecifier::DArg)
211    argIndex++;
212
213  if (k == ConversionSpecifier::InvalidSpecifier) {
214    // Assume the conversion takes one argument.
215    return !H.HandleInvalidPrintfConversionSpecifier(FS, Start, I - Start);
216  }
217  return PrintfSpecifierResult(Start, FS);
218}
219
220bool clang::analyze_format_string::ParsePrintfString(FormatStringHandler &H,
221                                                     const char *I,
222                                                     const char *E,
223                                                     const LangOptions &LO) {
224
225  unsigned argIndex = 0;
226
227  // Keep looking for a format specifier until we have exhausted the string.
228  while (I != E) {
229    const PrintfSpecifierResult &FSR = ParsePrintfSpecifier(H, I, E, argIndex,
230                                                            LO);
231    // Did a fail-stop error of any kind occur when parsing the specifier?
232    // If so, don't do any more processing.
233    if (FSR.shouldStop())
234      return true;;
235    // Did we exhaust the string or encounter an error that
236    // we can recover from?
237    if (!FSR.hasValue())
238      continue;
239    // We have a format specifier.  Pass it to the callback.
240    if (!H.HandlePrintfSpecifier(FSR.getValue(), FSR.getStart(),
241                                 I - FSR.getStart()))
242      return true;
243  }
244  assert(I == E && "Format string not exhausted");
245  return false;
246}
247
248//===----------------------------------------------------------------------===//
249// Methods on PrintfSpecifier.
250//===----------------------------------------------------------------------===//
251
252ArgTypeResult PrintfSpecifier::getArgType(ASTContext &Ctx,
253                                          bool IsObjCLiteral) const {
254  const PrintfConversionSpecifier &CS = getConversionSpecifier();
255
256  if (!CS.consumesDataArgument())
257    return ArgTypeResult::Invalid();
258
259  if (CS.getKind() == ConversionSpecifier::cArg)
260    switch (LM.getKind()) {
261      case LengthModifier::None: return Ctx.IntTy;
262      case LengthModifier::AsLong:
263        return ArgTypeResult(ArgTypeResult::WIntTy, "wint_t");
264      default:
265        return ArgTypeResult::Invalid();
266    }
267
268  if (CS.isIntArg())
269    switch (LM.getKind()) {
270      case LengthModifier::AsLongDouble:
271        // GNU extension.
272        return Ctx.LongLongTy;
273      case LengthModifier::None: return Ctx.IntTy;
274      case LengthModifier::AsChar: return ArgTypeResult::AnyCharTy;
275      case LengthModifier::AsShort: return Ctx.ShortTy;
276      case LengthModifier::AsLong: return Ctx.LongTy;
277      case LengthModifier::AsLongLong:
278      case LengthModifier::AsQuad:
279        return Ctx.LongLongTy;
280      case LengthModifier::AsIntMax:
281        return ArgTypeResult(Ctx.getIntMaxType(), "intmax_t");
282      case LengthModifier::AsSizeT:
283        // FIXME: How to get the corresponding signed version of size_t?
284        return ArgTypeResult();
285      case LengthModifier::AsPtrDiff:
286        return ArgTypeResult(Ctx.getPointerDiffType(), "ptrdiff_t");
287      case LengthModifier::AsAllocate:
288      case LengthModifier::AsMAllocate:
289        return ArgTypeResult::Invalid();
290    }
291
292  if (CS.isUIntArg())
293    switch (LM.getKind()) {
294      case LengthModifier::AsLongDouble:
295        // GNU extension.
296        return Ctx.UnsignedLongLongTy;
297      case LengthModifier::None: return Ctx.UnsignedIntTy;
298      case LengthModifier::AsChar: return Ctx.UnsignedCharTy;
299      case LengthModifier::AsShort: return Ctx.UnsignedShortTy;
300      case LengthModifier::AsLong: return Ctx.UnsignedLongTy;
301      case LengthModifier::AsLongLong:
302      case LengthModifier::AsQuad:
303        return Ctx.UnsignedLongLongTy;
304      case LengthModifier::AsIntMax:
305        return ArgTypeResult(Ctx.getUIntMaxType(), "uintmax_t");
306      case LengthModifier::AsSizeT:
307        return ArgTypeResult(Ctx.getSizeType(), "size_t");
308      case LengthModifier::AsPtrDiff:
309        // FIXME: How to get the corresponding unsigned
310        // version of ptrdiff_t?
311        return ArgTypeResult();
312      case LengthModifier::AsAllocate:
313      case LengthModifier::AsMAllocate:
314        return ArgTypeResult::Invalid();
315    }
316
317  if (CS.isDoubleArg()) {
318    if (LM.getKind() == LengthModifier::AsLongDouble)
319      return Ctx.LongDoubleTy;
320    return Ctx.DoubleTy;
321  }
322
323  switch (CS.getKind()) {
324    case ConversionSpecifier::sArg:
325      if (LM.getKind() == LengthModifier::AsWideChar) {
326        if (IsObjCLiteral)
327          return Ctx.getPointerType(Ctx.UnsignedShortTy.withConst());
328        return ArgTypeResult(ArgTypeResult::WCStrTy, "wchar_t *");
329      }
330      return ArgTypeResult::CStrTy;
331    case ConversionSpecifier::SArg:
332      if (IsObjCLiteral)
333        return Ctx.getPointerType(Ctx.UnsignedShortTy.withConst());
334      return ArgTypeResult(ArgTypeResult::WCStrTy, "wchar_t *");
335    case ConversionSpecifier::CArg:
336      if (IsObjCLiteral)
337        return Ctx.UnsignedShortTy;
338      return ArgTypeResult(Ctx.WCharTy, "wchar_t");
339    case ConversionSpecifier::pArg:
340      return ArgTypeResult::CPointerTy;
341    case ConversionSpecifier::ObjCObjArg:
342      return ArgTypeResult::ObjCPointerTy;
343    default:
344      break;
345  }
346
347  // FIXME: Handle other cases.
348  return ArgTypeResult();
349}
350
351bool PrintfSpecifier::fixType(QualType QT, const LangOptions &LangOpt,
352                              ASTContext &Ctx, bool IsObjCLiteral) {
353  // Handle strings first (char *, wchar_t *)
354  if (QT->isPointerType() && (QT->getPointeeType()->isAnyCharacterType())) {
355    CS.setKind(ConversionSpecifier::sArg);
356
357    // Disable irrelevant flags
358    HasAlternativeForm = 0;
359    HasLeadingZeroes = 0;
360
361    // Set the long length modifier for wide characters
362    if (QT->getPointeeType()->isWideCharType())
363      LM.setKind(LengthModifier::AsWideChar);
364    else
365      LM.setKind(LengthModifier::None);
366
367    return true;
368  }
369
370  // We can only work with builtin types.
371  const BuiltinType *BT = QT->getAs<BuiltinType>();
372  if (!BT)
373    return false;
374
375  // Set length modifier
376  switch (BT->getKind()) {
377  case BuiltinType::Bool:
378  case BuiltinType::WChar_U:
379  case BuiltinType::WChar_S:
380  case BuiltinType::Char16:
381  case BuiltinType::Char32:
382  case BuiltinType::UInt128:
383  case BuiltinType::Int128:
384  case BuiltinType::Half:
385    // Various types which are non-trivial to correct.
386    return false;
387
388#define SIGNED_TYPE(Id, SingletonId)
389#define UNSIGNED_TYPE(Id, SingletonId)
390#define FLOATING_TYPE(Id, SingletonId)
391#define BUILTIN_TYPE(Id, SingletonId) \
392  case BuiltinType::Id:
393#include "clang/AST/BuiltinTypes.def"
394    // Misc other stuff which doesn't make sense here.
395    return false;
396
397  case BuiltinType::UInt:
398  case BuiltinType::Int:
399  case BuiltinType::Float:
400  case BuiltinType::Double:
401    LM.setKind(LengthModifier::None);
402    break;
403
404  case BuiltinType::Char_U:
405  case BuiltinType::UChar:
406  case BuiltinType::Char_S:
407  case BuiltinType::SChar:
408    LM.setKind(LengthModifier::AsChar);
409    break;
410
411  case BuiltinType::Short:
412  case BuiltinType::UShort:
413    LM.setKind(LengthModifier::AsShort);
414    break;
415
416  case BuiltinType::Long:
417  case BuiltinType::ULong:
418    LM.setKind(LengthModifier::AsLong);
419    break;
420
421  case BuiltinType::LongLong:
422  case BuiltinType::ULongLong:
423    LM.setKind(LengthModifier::AsLongLong);
424    break;
425
426  case BuiltinType::LongDouble:
427    LM.setKind(LengthModifier::AsLongDouble);
428    break;
429  }
430
431  // Handle size_t, ptrdiff_t, etc. that have dedicated length modifiers in C99.
432  if (isa<TypedefType>(QT) && (LangOpt.C99 || LangOpt.CPlusPlus0x)) {
433    const IdentifierInfo *Identifier = QT.getBaseTypeIdentifier();
434    if (Identifier->getName() == "size_t") {
435      LM.setKind(LengthModifier::AsSizeT);
436    } else if (Identifier->getName() == "ssize_t") {
437      // Not C99, but common in Unix.
438      LM.setKind(LengthModifier::AsSizeT);
439    } else if (Identifier->getName() == "intmax_t") {
440      LM.setKind(LengthModifier::AsIntMax);
441    } else if (Identifier->getName() == "uintmax_t") {
442      LM.setKind(LengthModifier::AsIntMax);
443    } else if (Identifier->getName() == "ptrdiff_t") {
444      LM.setKind(LengthModifier::AsPtrDiff);
445    }
446  }
447
448  // If fixing the length modifier was enough, we are done.
449  const analyze_printf::ArgTypeResult &ATR = getArgType(Ctx, IsObjCLiteral);
450  if (hasValidLengthModifier() && ATR.isValid() && ATR.matchesType(Ctx, QT))
451    return true;
452
453  // Set conversion specifier and disable any flags which do not apply to it.
454  // Let typedefs to char fall through to int, as %c is silly for uint8_t.
455  if (isa<TypedefType>(QT) && QT->isAnyCharacterType()) {
456    CS.setKind(ConversionSpecifier::cArg);
457    LM.setKind(LengthModifier::None);
458    Precision.setHowSpecified(OptionalAmount::NotSpecified);
459    HasAlternativeForm = 0;
460    HasLeadingZeroes = 0;
461    HasPlusPrefix = 0;
462  }
463  // Test for Floating type first as LongDouble can pass isUnsignedIntegerType
464  else if (QT->isRealFloatingType()) {
465    CS.setKind(ConversionSpecifier::fArg);
466  }
467  else if (QT->isSignedIntegerType()) {
468    CS.setKind(ConversionSpecifier::dArg);
469    HasAlternativeForm = 0;
470  }
471  else if (QT->isUnsignedIntegerType()) {
472    CS.setKind(ConversionSpecifier::uArg);
473    HasAlternativeForm = 0;
474    HasPlusPrefix = 0;
475  } else {
476    llvm_unreachable("Unexpected type");
477  }
478
479  return true;
480}
481
482void PrintfSpecifier::toString(raw_ostream &os) const {
483  // Whilst some features have no defined order, we are using the order
484  // appearing in the C99 standard (ISO/IEC 9899:1999 (E) 7.19.6.1)
485  os << "%";
486
487  // Positional args
488  if (usesPositionalArg()) {
489    os << getPositionalArgIndex() << "$";
490  }
491
492  // Conversion flags
493  if (IsLeftJustified)    os << "-";
494  if (HasPlusPrefix)      os << "+";
495  if (HasSpacePrefix)     os << " ";
496  if (HasAlternativeForm) os << "#";
497  if (HasLeadingZeroes)   os << "0";
498
499  // Minimum field width
500  FieldWidth.toString(os);
501  // Precision
502  Precision.toString(os);
503  // Length modifier
504  os << LM.toString();
505  // Conversion specifier
506  os << CS.toString();
507}
508
509bool PrintfSpecifier::hasValidPlusPrefix() const {
510  if (!HasPlusPrefix)
511    return true;
512
513  // The plus prefix only makes sense for signed conversions
514  switch (CS.getKind()) {
515  case ConversionSpecifier::dArg:
516  case ConversionSpecifier::iArg:
517  case ConversionSpecifier::fArg:
518  case ConversionSpecifier::FArg:
519  case ConversionSpecifier::eArg:
520  case ConversionSpecifier::EArg:
521  case ConversionSpecifier::gArg:
522  case ConversionSpecifier::GArg:
523  case ConversionSpecifier::aArg:
524  case ConversionSpecifier::AArg:
525  case ConversionSpecifier::rArg:
526    return true;
527
528  default:
529    return false;
530  }
531}
532
533bool PrintfSpecifier::hasValidAlternativeForm() const {
534  if (!HasAlternativeForm)
535    return true;
536
537  // Alternate form flag only valid with the oxXaAeEfFgG conversions
538  switch (CS.getKind()) {
539  case ConversionSpecifier::oArg:
540  case ConversionSpecifier::xArg:
541  case ConversionSpecifier::XArg:
542  case ConversionSpecifier::aArg:
543  case ConversionSpecifier::AArg:
544  case ConversionSpecifier::eArg:
545  case ConversionSpecifier::EArg:
546  case ConversionSpecifier::fArg:
547  case ConversionSpecifier::FArg:
548  case ConversionSpecifier::gArg:
549  case ConversionSpecifier::GArg:
550  case ConversionSpecifier::rArg:
551    return true;
552
553  default:
554    return false;
555  }
556}
557
558bool PrintfSpecifier::hasValidLeadingZeros() const {
559  if (!HasLeadingZeroes)
560    return true;
561
562  // Leading zeroes flag only valid with the diouxXaAeEfFgG conversions
563  switch (CS.getKind()) {
564  case ConversionSpecifier::dArg:
565  case ConversionSpecifier::iArg:
566  case ConversionSpecifier::oArg:
567  case ConversionSpecifier::uArg:
568  case ConversionSpecifier::xArg:
569  case ConversionSpecifier::XArg:
570  case ConversionSpecifier::aArg:
571  case ConversionSpecifier::AArg:
572  case ConversionSpecifier::eArg:
573  case ConversionSpecifier::EArg:
574  case ConversionSpecifier::fArg:
575  case ConversionSpecifier::FArg:
576  case ConversionSpecifier::gArg:
577  case ConversionSpecifier::GArg:
578    return true;
579
580  default:
581    return false;
582  }
583}
584
585bool PrintfSpecifier::hasValidSpacePrefix() const {
586  if (!HasSpacePrefix)
587    return true;
588
589  // The space prefix only makes sense for signed conversions
590  switch (CS.getKind()) {
591  case ConversionSpecifier::dArg:
592  case ConversionSpecifier::iArg:
593  case ConversionSpecifier::fArg:
594  case ConversionSpecifier::FArg:
595  case ConversionSpecifier::eArg:
596  case ConversionSpecifier::EArg:
597  case ConversionSpecifier::gArg:
598  case ConversionSpecifier::GArg:
599  case ConversionSpecifier::aArg:
600  case ConversionSpecifier::AArg:
601    return true;
602
603  default:
604    return false;
605  }
606}
607
608bool PrintfSpecifier::hasValidLeftJustified() const {
609  if (!IsLeftJustified)
610    return true;
611
612  // The left justified flag is valid for all conversions except n
613  switch (CS.getKind()) {
614  case ConversionSpecifier::nArg:
615    return false;
616
617  default:
618    return true;
619  }
620}
621
622bool PrintfSpecifier::hasValidThousandsGroupingPrefix() const {
623  if (!HasThousandsGrouping)
624    return true;
625
626  switch (CS.getKind()) {
627    case ConversionSpecifier::dArg:
628    case ConversionSpecifier::iArg:
629    case ConversionSpecifier::uArg:
630    case ConversionSpecifier::fArg:
631    case ConversionSpecifier::FArg:
632    case ConversionSpecifier::gArg:
633    case ConversionSpecifier::GArg:
634      return true;
635    default:
636      return false;
637  }
638}
639
640bool PrintfSpecifier::hasValidPrecision() const {
641  if (Precision.getHowSpecified() == OptionalAmount::NotSpecified)
642    return true;
643
644  // Precision is only valid with the diouxXaAeEfFgGs conversions
645  switch (CS.getKind()) {
646  case ConversionSpecifier::dArg:
647  case ConversionSpecifier::iArg:
648  case ConversionSpecifier::oArg:
649  case ConversionSpecifier::uArg:
650  case ConversionSpecifier::xArg:
651  case ConversionSpecifier::XArg:
652  case ConversionSpecifier::aArg:
653  case ConversionSpecifier::AArg:
654  case ConversionSpecifier::eArg:
655  case ConversionSpecifier::EArg:
656  case ConversionSpecifier::fArg:
657  case ConversionSpecifier::FArg:
658  case ConversionSpecifier::gArg:
659  case ConversionSpecifier::GArg:
660  case ConversionSpecifier::sArg:
661    return true;
662
663  default:
664    return false;
665  }
666}
667bool PrintfSpecifier::hasValidFieldWidth() const {
668  if (FieldWidth.getHowSpecified() == OptionalAmount::NotSpecified)
669      return true;
670
671  // The field width is valid for all conversions except n
672  switch (CS.getKind()) {
673  case ConversionSpecifier::nArg:
674    return false;
675
676  default:
677    return true;
678  }
679}
680